Ammonia Decomposition Promoted by the Formation of Ternary Transition Metal Nitride Intermediates: Ni (Co)-Loaded BaSi ₂

Catalytic ammonia decomposition for hydrogen release at reduced temperatures is a critical component of the hydrogen energy roadmap. However, conventional nonprecious transition metal (TM) catalysts, such as Ni and Co, typically suffer from a high energy barrier in the N-N coupling step. In this study, we report that a stable Zintl phase silicide of BaSi₂ functions as an efficient support for Ni and Co catalysts in ammonia decomposition via the formation of TM-nitrogen-barium intermediates at the TM-BaSi₂ interface. Characterizations using kinetic studies, X-ray photoelectron spectroscopy (XPS), and density functional theory calculations suggest that electron transfer occurs from the interfacial low-valence barium to nitrogen atoms bonded to TM at the TM-BaSi₂ interface, which leads to the formation of TM-nitrogen-barium intermediates and in turn lowers the energy barrier for the rate-determining N-N coupling step. This promotion enables Ni- or Co-loaded BaSi₂ catalysts to significantly outperform conventional nonprecious metal catalysts and become comparable to the Ru-based catalysts. These results offer a new perspective for the future design of nonprecious metal catalysts for ammonia decomposition at reduced temperature.